In a recent column I mentioned that it's a good idea to label all your drives and drive connectors in your RAID 5 array. That way when a drive fails you won't make the mistake of pulling the wrong drive from the array and hosing your data.

Today, I want to provide you with another tip on preventing potential problems with RAID arrays. The tip comes to me courtesy of a colleague who had the following experience. About a year ago he bought a bunch of hard drives of the same make and model from a vendor so he could build an array for his system. Unfortunately, within a year half of his drives had failed and needed replacing. How could that be? Was it just bad luck?

After investigating the problem, my colleague discovered that the drives he purchased had consecutive serial numbers which means that they all came from the same manufacturing lot. After discussion with colleagues about the matter, it turned out that this was not an isolated incident. In fact, using drives from the same manufacturing lot in an array can often be a recipe for disaster as it can drastically increase the failure rate of drives if your drives happen to come from a bad batch of drives.

What's the lesson here? Mix and match a bit with the drives in your arrays, and avoid whenever possible using drives from the same manufacturing lot. And to be safe, implement RAID 6 that allows recovery from two failed drives instead of the one failed drive that RAID 5 protects you against.